The present invention relates to radiation-curable compositions comprising a cationically curable compound and a free radical polymerizable compound. The compositions, after cure, have improved clarity. One aspect of the invention concerns forming three-dimensional objects by rapid prototyping the present compositions.
Cationically polymerizable compositions, such as epoxy based polymerizable compositions, are capable of producing articles having high image accuracy. However, due to the relatively slow cure of the cationically curable compositions it is often necessary to prepare hybrid compositions, i.e. mix the cationically curable compounds with relatively fast curing free radical polymerizable compounds. Examples of such hybrid compositions are set forth in, for instance, U.S. Pat. Nos. 5,972,563; 5,468,748; 5,468,749; 5,707,780; and Canadian Patent 2,171,504. Although the addition of free radical polymerizable components helps improve the image accuracy, it typically results in cured products having low or no transparency and a frequently whitish appearance. These disadvantages can be particularly pronounced in products comprising fairly thick layers (or a multitude of consecutive thin layers) of the cured composition, making these hybrid compositions unpreferred or even unsuitable for a wide variety of applications.
It is an object of the present invention to provide radiation-curable hybrid compositions that result, upon cure, in products having an improved clarity. In particular, an object of the invention is to provide a composition for forming, via rapid prototyping, 3-dimensional objects having improved clarity.
In one embodiment, the present invention provides a composition comprising:
(i) a cationically polymerizable component, preferably an epoxy component, more preferably a cyclohexeneoxide component;
(ii) a first free radical polymerizable component selected from the group consisting of:
(a) non-aromatic free radical polymerizable components comprising a C1-C10 ether group, preferably at least two C2-C4 ether groups; and
(b) aromatic free radical polymerizable components comprising more than four C1-C10 ether groups, preferably at least 8 C2-C4 ether groups, and
(iii) a second free radical polymerizable component, preferably a free radical polymerizable component comprising at least three (meth)acrylate groups;
wherein the composition has a clarity ratio greater than 1.03.
Another embodiment of the present invention provides a composition comprising
(i) a cationically polymerizable component, and
(ii) a free radical polymerizable component other than caprolactone acrylate,
wherein the composition, after cure, has a clarity of at least 90%.
The present invention also provides processes, e.g. a rapid prototyping process, for curing the present compositions. In addition, the present invention provides objects, e.g. three dimensional objects, obtained by such processes.
In yet a further embodiment, the present invention provides a process for improving, by more than a factor 1.03, the clarity of a product obtained by curing a hybrid composition. The process comprises:
(i) adding, prior to curing, a compatible free radical polymerizable component to the hybrid composition.
Suitable compatible free radical polymerizable components for this process include, for instance, components selected from the group consisting of:
(a) non-aromatic free radical polymerizable components comprising a C1-C10 ether group, preferably at least two C2-C4 ether groups; and
(b) aromatic free radical polymerizable components comprising more than four C1-C10 ether groups, preferably more than four C2-C4 ether groups; and
(c) hydroxyfunctional free radical polymerizable ester components.